This invention relates to a light-emitting diode and a method of manufacturing the same, and more particularly to a light-emitting diode having a hetero-junction of aluminum gallium arsenide structure and a method of manufacturing the same.
Compound semiconductor materials, such as gallium arsenide and aluminum gallium arsenide (Al.sub.x Ga.sub.1-x As), have been widely used as a semiconductor light source, e.g., a light-emitting diode, etc. by utilizing their light-emitting function. For example, light-emitting diodes are made from a wafer which comprises a p-n junction formed by a plurality of epitaxial layers grown on a single crystal substrate by Liquid Phase Epitaxy (LPE), Metal Organic Vapor Phase Epitaxy (MOVPE), etc.
A conventional light-emitting diode having a double-hetero structure of Al.sub.x Ga.sub.1-x As (0.ltoreq.x.ltoreq.1) layers comprises a p-type gallium arsenide substrate, and three epitaxial layers of Al.sub.x Ga.sub.1-x As, which are a cladding layer of p-type Al.sub.x11 Ga.sub.1-x11 As, an active layer of Al.sub.x22 Ga.sub.1-x22 As, and a window layer of Al.sub.x33 Ga.sub.1-x33 As. These epitaxial layers are formed on the substrate, in order, by growing from three different growth melts. In this case, the mixed crystal ratios of aluminum to arsenic x11, x22, x33 of the layers meet the condition that:
x11&gt;x22; x33&gt;x22. PA1 wherein x1, x2, x3 and x4 represent mixed crystal ratios of aluminum to arsenic of the layers, respectively, and meet the condition that: PA1 x2.gtoreq.x4&gt;x1.gtoreq.x3(0.ltoreq.x1, x2, x3, x4.ltoreq.1). PA1 epitaxially growing an intervening layer on a substrate of gallium arsenide from a first growth melt doped with at least one p-type dopant; PA1 epitaxially growing a cladding layer on the intervening layer from a second growth melt doped with less than a predetermined amount of dopant; PA1 epitaxially growing an active layer on the cladding layer from the first growth melt; and PA1 epitaxially growing a window layer on the active layer from the second growth melt, the second growth melt being subsequently doped with at least one n-type dopant after the growth of the intervening layer, the dopant being sufficient to turn the type of conductivity of the second growth melt into n-type; PA1 wherein the at least one p-type dopant in the cladding layer is thermally diffused from the intervening layer by subsequent epitaxial growths of the active layer and the window layer so as to invert the initial type of conductivity of the cladding layer to p-type.
While the ratio x22 may be determined depending on a desired wavelength, the ratios x11 and x33 are preferably determined so that the differences between x11 and x22, and between x33 and x22, i.e. x11-x22 and x33-x22 are as large as possible, in view of making injection of minority carriers more efficient by the hetero junction structure, and facilitating recombination of injected carriers caused by the confinement of the carriers.
For particular light-emitting diodes, such as a light-emitting diode lamp, the output power of such light-emitting diodes is preferably higher than that of other types of diodes. To obtain these characteristics, the aforementioned mixed crystal ratios of aluminum to arsenic x11 and x33 are necessarily higher. In the conventional light-emitting diode, however, there is a disadvantage in that such light-emitting diodes having higher mixed crystal ratios of aluminum to arsenic are more likely to be deteriorated under a highly moist environment. Because the higher the mixed crystal ratios of the epitaxial layers are, the more likely the epitaxial layers are to be oxidized under the environment. To solve this problem, for example, the light-emitting diode chip may be molded by a particular resin material having low moisture absorption characteristics. However, such a measure is still insufficient, because since a thinner layer of molding resin is required for a thin light-emitting diode lump, the more limited environments it can be applied to.